Unwanted links and ads appearing in site

Hello everyone,

I recently launched a WordPress site for a client. I checked it out thoroughly in different browsers, resolutions etc. Everything appears to be running smoothly.

Now, the client is reporting that he sees unwanted links and ads appearing on the site. The type of annoying links that you see on spam blogs. Words that were NOT coded to be links are appearing to him as links taking him to other sites and advertisements, or he mouses over certain words and pop-up ads appear. I have not seen any of these issues on my end, and I checked my source code for unwanted links thinking my WP system got hacked. I saw nothing. To the best of my knowledge, nobody else has seen these issues.

Does anyone know what the problem could be? Could the clients computer have been hacked? Could it be some type of BHO virus that was installed in their browser without them knowing? Or perhaps some annoying IE BHO that they havent disabled?

Any suggestions or information would be appreciated. Thanks!